Abstract
Malignant psoas syndrome is caused by a malignant tumor infiltrating the psoas muscle and is characterized by severe pain. Currently, no definitive diagnostic or therapeutic approaches have been established for this condition. Although multiple medications are often used for pain relief, pain management can often be challenging, and there are various treatment options. Here, we report a case of a Japanese man in his 60s who was diagnosed with malignant psoas syndrome due to metastasis of myxoid liposarcoma. Despite undergoing several pharmacological treatments for severe pain, their effects were insufficient. Palliative radiation therapy was therefore planned and started to relieve pain. We discussed radiation therapy methods. Since there was no previous literature on treatment with single doses exceeding 3 Gy and the attending physician expected the patient to have a little longer survival time, we decided to treat 39 Gy in 13 fractions of radiation therapy. Early pain relief was achieved with 24 Gy in eight fractions. Radiation therapy was continued without change after the pain improved. The treatment was terminated at 36 Gy in 12 fractions due to the deterioration of the patient's general condition caused by the progression of metastases throughout the body. The patient died two days after the end of his treatment (18 days after the start of radiation therapy) due to exacerbation of his primary disease. No adverse events related to radiation therapy were observed. In this case, radiation therapy was found to be effective at an early stage in relieving pain from malignant psoas syndrome, which was difficult to control with multiple pharmacological treatments. Given its effectiveness in early pain relief without adverse events, radiation therapy should be actively considered as a treatment option for malignant psoas syndrome.